Chemical process and product



2,739,074 CHEMICAL PRGCESS AND PRODUCT Ralph K. Iler, Wilmington, Del., assignor to E. I. du Pont de Nemours and Company, Wilmington, Del., a corporation of Delaware No Drawing. Application March 6, 1952, Serial No. 275,232

; 7 Claims. (Cl. 106-308) This invention relates to surface-modified siliceous particles and to processes for making them. The invention is more particularly directed to inorganic siliceous particles having an average specific surface area of at least 1 square meter per gram, having chemically bound to the silicon atoms on the surface of said particles at least 100 OR groups per 100 square millimicrons of surface area of the siliceous solid, where R is a substituted hydrocarbon radical in which the carbon attached to oxygen is also attached to at least one hydrogen atom, said substituted hydrocarbon radical having a neutralreacting electron donor atom attached to a carbon atom at least 1 carbon atom removed from the oxygen atom of the OR group, the electron donor atom being selected from the class consisting of nitrogen, oxygen and halogens having an atomic number above 9, each R radical having from 2 to 18 carbon atoms.

This application is a continuation-in-part of my copending U. S. application, Serial No. 130,343, filed November 30, 1949, now abandoned.

I have found that when dense particles of inorganic siliceous material having an average specific surface area of at least 1 square meter per gram are chemically reacted with a substituted primary or secondary monohydric alcohol having from 2 to 18 carbon atoms and containing a neutral-reacting electron donor substituent group attached to a carbon atom at least 1 carbon atom removed from the hydroxyl group, the substituent group containing one or more electronegative atoms selected from the class consisting of nitrogen, oxygen and halogens having an atomic number above 9, the alcohol reacts preferentially through the hydroxyl group effecting surface esterification.

The products of my invention are a specific kind of siliceous solids. Some of these products I refer to hereafter as estersils. Estersils are solids made by chemically reacting alcohols with certain supercolloidal siliceous solids. The reaction I have called esterification and the chemically bound OR groups containing a neutral-reacting electronegative atom resulting therefrom I have called substituted ester groups.

For a detailed description of estersils prepared from primary and secondary unsubstituted monohydric alcohols, reference is made to my aforementioned copending U. S. application, Serial No. 171,759, filed July 1, 1950, now abandoned, or to my United States Patent 2,657,149, issued October 27, 1953, as a continuation in part of said application Serial No. 171,759, in which estersils of that class are claimed.

The materials used to form the skeleton or internal structure, the so-called substrate, of the products of my invention are solid inorganic siliceous materials. They contain substantially no chemically bound organic groups. They have reactive surfaces which I believe to result from surface silanol (SiOH) groups. The substrate mate- They can They can be water-insoluble metal They can be Water-insoluble metal silicates rials can be mineral or synthetic in origin. be amorphous silica. silicates.

Patented Mar. 20, 1956 coated with amorphous silica. They can be water-insoluble metal silicates coated with amorphous silica.

For the purposes of this invention the substrate particles should have an average diameter greater than about 1 millimicron. Substrate particles in which the ultimate units have diameters of at 1east15 millimicrons but less than millimicrons are preferred. Another preferred type of substrate particles are supercolloidal aggregates or pulverulent solids.

It is further preferred that the inorganic siliceous solids be porous, that is, they should have exposed surfaces in the interior of the particle which are available to the exterior so that liquids and gases can penetrate the pores and reach the exposed surfaces of the pore Walls. In other Words, the solid forms a three-dimensional network or webwork through which the pores. or voids or interstices extend'as a labyrinth of passages or open spaces.

Especially preferred are porous inorganic siliceous solids having average pore diameter of at least four millimicrons. The large pores afford easy access for alcohol molecules in the subsequent esterification to give the products of the invention.

The substrate particles have large surface areas in relation to their mass. The term used herein and the one normally so used in the art to express the relationship of surface area to mass is specific surface area. Numerically, specific surface area will be expressed in square meters per gram (m. /g.).

According to the present invention, the subtrate particles have an average specific surface area of at least 1 square meter per gram and preferably the average specific surface area is at least 25 m. /g. In the case of precipitated amorphous silica, a preferred material, there is an optimum range of about 200 to 400 m. /g., based on the fact that in this range the supercolloidal particles or aggregates can be obtained in a dry state without bringing about a considerable collapse of the porous structure, by replacing the Water with a Watermiscible organic solvent such as acetone and then mying. This powder is especially suitable for subsequent esterification. It is, of course, possible to produce very voluminous aerogels by processes of the prior art, having surface areas of from 200 to 900 m. /g. Such highly porous forms of silica can be surface-esterified by the process of this invention.

Specific surface area, as referred to herein, is determined by the accepted nitrogen adsorption method described in an article A new method for measuring the surface areas of finely divided materials and for determining the size of particles by P. H. Emmett in Symposium on New Methods for Particle Size Determination in Sub-Sieve Range published by the American Society For Testing Materials, March 1951, page 95. The value of 0.162 square millimicron for the area covered by one surface adsorbed nitrogen molecule is used in calculating the specific surface areas.

Pore diameter values are obtained by first determining pore volumefrom nitrogen adsorption isotherms as described by Holmes and Emmett in Journal of Physical and Colloid Chemistry 51, 1262 (1947). From the volume figure, the diameters are obtained by simple ge-,

For materials having a particle size in the range of from 2 .or 3 microns down to 5 millimicrons, the electron microscope is used. Particle size determination using an electron microscope is described in detail by J. H. L. Watson in Analytical Chemistry--20, 5'76 (1948) While various inorganic siliceous solids having the aforementioned properties can be used as substrate materials in preparation of the products of my invention, precipitated amorphous silica is particularly preferred. Such silica is characterized by X-rays as lacking crystalline structure.

The preparation of several suitable amorphous silicas is illustrated in the examples. Fora detailed discussion of sources of amorphous silica for use in preparing estersils of primary and secondary alcohols, reference should be had to my copending U. S. application serial No. 171,- 579, filed July'l, 1950, now abandoned.

Instead of silica, water-insoluble metal silicates can be used as the substrate. Such metal silicates can be prepared, as is Wellknown in the prior art, by treatment of silicas with metal salts or hydrous metal oxides, excluding those containing only alkali metal ions. Such metal silicates can 'be'prepared so as to have a large number of silanol (--SiOH-) groups on 'the surface of the particle.

Thus metal silicates having a large proportion of metal ions on the surface may be activated for esterification by washing with acids to remove at least a portion of the metal ion and leave surface silanol'groups.

Crystalline metal silicates occurring in nature can also be used. However, the proportion of silanol groups on most minerals is very small'since the surfaces also contain metal hydroxy groups, silicon oxygen groups and adsorbed metal ions. Therefore, before esterification it is necessary to introduce silanol groups on the surface. Loosely adsorbed metal ions maybe exchanged for hydrogen ions by washing the dilute acids or by treatment with ion exchange resins. In some cases, more vigorous treatment, such as reaction with acids at low pH and, often at elevated temperatures are required to give a material which will'contain a sufiicient number of silanol groups in the surface to yield an organophilic product on esterification.

Alternatively or additionally, silanol groups can be introduced on the surface of metal silicates by coating them with a layer of amorphous silica. This is accomplished by treating, say, sodium silicate with an acid in the presence of the mineral silicate particles under such conditions that the silica for tried will deposit as a coating on the mineral particle.

M n ral r st l n sili ates h h c e used in P r paring the substrate particles are as follows: the asbestos e a u h s q y ptilc asbe t and s pent (hydrous magnesium silicate) and amphiboles such as crocidolite asbestos (a sodium magnesium iron silicate), amosite (an iron silicate), tremolite (a calcium magnesium silicate), and anthothyllit (a magnesium iron silicate); clay materials, Such as halloysite.(an aluminum siliat at pu g te magnesiu a m n m Silicate), torite (a magnesium lithium silicate), nontronite (magnesium aluminum iron silicates); the kaolins, such as kaolinite, a c an d sk tc luminum s l a a bentonites, such as beidillite, saponite and montmorilonite (magnesium aluminum iron silicates); and micaceous minerals, su h as a l op tc (a pQ a s a n um a m n m sil e). maceapo ssi m aluminu si biotite (a potass um on 31 s l cat and ermi u (a hyd ou masuc ium m lu num silia ESTERLFYING AGENT The inorganic siliceous solid-s described above are reacted with substituted primary and secondary monohydric alcohols to give, the products of the invention. The alcohols. ein all este y n agents are. t p ,ese t xiv by the formula ROH he R is a sub t tuted ydr car o radical in which the carbon atom attached to the oxygen of the hydroxyl group is also attached to at least one hydrogen, the hydrocarbon radical having from 2 to 18 carbon atoms and containing a neutral-reacting electron donor substituent group which is attached to a carbon atom at least 1 carbon atom removed from the hydroxyl group, said substituent group containing an electronegative atom selected from the class consisting of nitrogen, oxygen and halogens having an atomic number above 9.

By neutral-reacting substituents I mean groups which are neither substantially acidic nor basic in their chemical reactivity. In other words, the groups are substantially neutral. And by the term substantially neutral I mean that when the purified substituted alcohol is placed in Water the electronegative groups of the alcohol are sufficiently neutral that the pH as measured by immersing the glass electrode in a 1% solution of the alcohol in water will give an apparent pH reading between about 5 and 8. Boiled distilled water should be employed in order to remove the carbon dioxide present in the water. If the substituted alcohol is not readily soluble in water, it may be necessary to carry out the pH determination'in the presence of a 50-50 mixture of water and methanol.

The term electron donor substituent as used herein means functional groups containing an atom selected from the class consisting of nitrogen, oxygen, chlorine, bromine and iodine. Each member of this class is well'known to contain at least one pair of unshared electrons capable of participating in a coordinate-covalent type bond (also referred to as dative or donor-acceptor type bond) such as, for example, in a hydrogen bond.

It is to be understood that alcohols containing oxygen as an electron donor substituent group will be monohydric, that is, the additional oxygen 210m Will not be present as a functional alcoholic group. Thus, for example, it may be present as in an ester, ether or carbonyl group.

Examples of esterifying agents which can be used in a process of the invention include Z-nitroethanol, 3-chloropropanol, Z-brornoethanol, the monobutyl ether of ethylene glycol, monobutyl ether of diethylcne glycol, N,N- dimethyl .hydroxyacetamide, diacetone alcohol, ethylene glycol monoacetate, ethylene glycol monostearate, ethyl hydroxyacetate, glycollonitrile, priodobenzyl alcohol, 2,4- dichlorobenzyl alcohol, hydroxypropionitrile, ethylene chlorhydrin,v acetoacetic ester, p-nitrobenzyl alcohol and hydroxy'ethyl methacrylate.

Technically, there is no upper limit to the number of carbon atoms which may be present in the esterifying agent. As a practical matter, however, thegroup of alcohols having from 2 to' 18 carbon atoms include the majority of commercially available alcohols and offer a selection of molecule sizes which should be adequate for any purpose.

Substituted alcohols containing from 3 to. 8 carbon atoms are especially preferred because they are relatively low boiling liquids which are most readily handled in the process. When present as unreacted. excess they canbe most. readily removed from the esterified product by drying in a vacuum oven, without the necessity of extraction procedure. Additionally, they are also the most e onomical to use and yield a product having a low ratio of organic matter to silica.

Another class of preferred esterifying agents are those Which contain nitrogen as the electron donor atom. lude alCQhQls Containing nitrile, nitro, nitroso, amide or azo groups. It will be understood that alcohols containing primary, secondary or tertiary amino groups are outside the scope of this invention since they are markedly basic in their chemical reactivity.

The esterifying agent will ordinarily contain only one electron donor substituent group, but the agent can contain more than one group. For instance, a dior multiple chlorinated monohydric alcohol, for example, 2,4-dichlorobenzyl alcohol can be employed. The ou s do. not necessari y nee t b he a The same group may contain two electr'on'egative atoms, for instance, an amide group which contains both an oxygen and a nitrogen atom.

The esterifying agent need not be a single alcohol. Mixtures of substituted alcohols can be used. Thus, when a variety of surface properties is desired, a mixture of alcohols may be used provided, of course, that they are compatible with one another. Also there can be a mixture of different chain lengths found in the technical grade of some alcohols. And, if desired, a mixture consisting of an unsubstituted primary or secondary alcohol and an alcohol containing a neutral electron donor atom can be used.

ESTERIFICATION The siliceous substrate to be reacted with the alcohol containing the electron donor group should contain surface silanol groups. Pure amorphous silica which has been in contact with moisture has such a surface. The surface must not be covered with other materials which block access to the silanol group. Metal ions on the surface of metal silicates must be exchanged for hydrogen atoms. This can be done by treatment with a hydrogen form of a cation exchange-resin or by treatment with an acid as mentioned heretofore. Alternatively, the particles can be coated with a thin layer of silica. The external surface can then be reacted with alcohol.

The inorganic siliceous solid is preferably freed of extraneous material before esterification, and the pH is adjusted to avoid strong acids or alkalis in the reaction. The pH is preferably 5 to 8.

The amount of water present in the reacting mass during the esterification step has an important bearing on the degree of esterification that Will be obtained. Thus, since the esterification process is an equilibrium reaction, it is ordinarily desirable to keep the water content as low as possible during the course of the reaction.

In order to esterify sutficiently to obtain a high proportion of substituted ester groups on the surface of the siliceous particles, the water in the liquid phase of the system should not exceed about 5% by Weight of that phase. For maximum esterification, the water content must be kept below about 1.5%. As already mentioned, it is desirable to keep the water content as low as possible.

Because of the hindering effect of water on the esterification, if the siliceous solid to be esterified is wet, the free water must be removed either before the solid is put into the alcohol or alternatively it may be removed by distillation after mixing with the alcohol.

Simple air drying at temperatures of from 100 to 150 C. will remove most of the free water. Drying may be hastened by the application of vacuum. For many types of siliceous solids, however, air drying is not satisfactory because they tend to shrink to hard, compact masses upon drying from water.

Water can suitably be removed from a wet siliceous solid before esterification by displacing the water in the wet mass with a polar organic solvent such as acetone. The solvent can later be recovered.

Preferably, water is removed from wet siliceous solids prior to esterification by azeotropic distillation. Thus, water-wet cake can be mixed with a polar organic solvent such as methyl ethyl ketone and the mixture distilled until the system is freed from Water. The or ganic solvent can then be evaporated to give a dry product for reaction with alcohol.

Alternatively, the alcohol which is to be used as the esterifying agent can also be used in some instances as the azeotropic dehydrating agent.

The ratio of alcohol and siliceous material to be used in the esterification is limited only by the fact that the alcohol should be present in sufficient excess to facilitate a practical rate of reaction. Preferably, sufficient alcohol is used to provide a slurry of the siliceous material inalcohol which can be readily stirred. Of course, larger portions of alcohol must be used when no water is removed from the system during the reaction. The reason for'this being that the reaction liberates water and may exceed the maximum permissible value unless alcohol is added either before or during the reaction step.

In general, it is suHicient to carry out the esterification by simply refluxing the mixture of the silica and the alcohol together for a suitable length of time, for example, upwards of 2 hours. In cases where the alcohol is somewhat unstable, it may be desirable to carry out the esterification at somewhat lower temperatures than the boiling point of the alcohol in order to prevent the excessive decomposition in the liquid phase. A preferred method of using unstable alcohols as esterifying agents comprising heat-activating the siiica and chemically reacting the alcohol with the surface-activated silica in accordance with the invention described and claimed in the copending application of Max T. Goebel, Serial No. 261,140, filed December 11, 1951.

In addition, when the alcohol to be used is rather low boiling, that is, less than C., in order to promote more complete reaction than could be realized at the boiling point, it may be desired to carry out the esterification in the autoclave at temperatures of from 200300 C.

The extent of the reaction is fixed more by the temperature than by the time, that is, at a suitable temperature the esterification reaction proceeds quite rapidly up to a certain point which is characteristic of the temperature and of the alcohol and thereafter proceeds slowly.

The minimum reaction time and temperature in order to obtain any given extent of reaction varies with the alcohol used. While it is difiicult to set forth in great detail the relationship between the temperature required for any given extent of reaction and the structure of the alcohol, one skilled in the art may learn from the data the general principles involved and conclude what conditions should be used for another alcohol.

The temperatures substantially below about 100 C. are not suitable in most instances. Alcohol can be adsorbed on the siliceous surface at such temperatures but true esterification is not obtained.

The esterifying temperature should not exceed the thermal decomposition point of the alcohol while in the presence of siliceous solids. Nor should it exceed the point of thermal stability of the esterified siliceous materials. Preferably, the heating is not prolonged any more than is required to achieve esterification equilibrium.

As already indicated, the reaction between amorphous silica and liquid alcohols can be carried out by autoclav ing a slurry of the silica in an excess of the organic reagent. However, when the alcohol is high melting, or unstable above its melting point, it is preferred to carry out the reaction in a dilute solution, say, 10% of the organic reagent in an inert solvent, such as, for instance, benzene, toluene, xylene, trichloroethylene, dioxane and dibutyl ether of ethylene glycol.

Whether the reaction is efiected at atmospheric pressure at the reflux temperature of the solution or under autoclave conditions will largely depend on the boiling point of the solvent used; that is, whether the boiling point is high enough to effect substantial reaction between the silica and the esterifying agent. Occasionally, it is desirable to deposit a mono layer of the alcohol uniformly over the silica surface by stirring the latter with a solution of the alcohol in a low boiling inert solvent such as ether or acetone, and then evaporating the solvent while maintaining constant agitation. Complete reaction is then efiected by heating the dry, coated product to a temperature sufliciently high to cause removal of Water.

After completion of the esterification, the estersils can be removed from the unreacted alcohol by conventional methods. Thus, the separation .can be made by filtration in those instances where the estersi'ls consist of particles of supercolloidal size, the particles being retained on ordinary filter media.

Alternatively, the alcohol can be vaporized by applying vacuum to the reaction vessel. Or where the alcohol is one which will distill at atmospheric pressure without decomposition, simple distillation can be used. In the case .of higher alcohols which are not readily distilled. except under very high vacuum, the alcohol can be extracted from the product with a low boiling solvent such as, for instance, methyl ethyl lretone, chloroform orether.

PROPERTIES AND USES OF THE PRODUCTS The products of the invention .are in the form of powders or sometimes lumps or cakes which are pulverable under the pressure of the finger or by a light rubbing action. The esterified inorganic siliceous solids are generally exceedingly fine, light, fluffy, voluminous powders.

The esterification reaction does not substantially change the structure of the inorganic siliceous solid or substrate which was esterified. In other words, the internal structure of the estersil, the structure to which the OR groups are chemically bound, has substantially the same particle size, surface area and other characteristics described previously in the discussion of the substrate material. The estersils of the invention are in a colloidal or a supercolloidal state of subdivision.

The products of the invention can be hydrophilic, organophilic or hydrophobic depending on the degree of esterification and also on the type and number of electron donor substituents per OR group. The presence of the electron donor substituent can be demonstrated by chemical analysis. The surface properties of the resultant estersils reflect the presence of the electron donor substituent on the surface.

By the term organophilic I means that when a pinch of estersil is shaken in a two phase liquid system of water and n-butanol in a test tube the produce will wet into the n-butanol phase in preference to the water-phase.

In the case of the preferred alcohols, it is possible to force more than 270 alcohol molecules, say 300 to 400, to react per 100 square millimicrons of surface area of the siliceous substrate by using severe reaction conditions, care being taken not to decompose the alcohol or the resulting substituted ester groups.

The number of ester groups for 100 square millimicrons of siliceous substrate surface is calculated from the expression: 1

where C is the weight of the carbon in grams attached to 100 grams of substrate; 11 is the number of carbon atoms in the OR groups; Sn is the specific surface area in m. g. of the substrate as determined by nitrogen adsorption.

Where the sample to be analyzed is one in which the type of alcohol is unknown, the sample can be decomposed with an acid and the alcohol can be recovered and identified. The specific surface area of the substrate can be determined by first burning off the ester groups, as for example, by slowly heating the estersil in a stream of oxygen up to 500 C. and holding it at that temperature for a period of about three hours and then rehydrating the surface of the particles by exposure to 100% relative humidity at room temperature for several hours and finally determining the surface area of the remaining solid by nitrogen adsorption method.

In the products of the invention the OR groups are chemically bound to the substrate. The products should not be confused with compositions in which an alcohol Surface area:

is merely, physically adsorbed on the surface o h siliceous solid. Adsorbed alcohols can be removed by heating the material at relatively low temperature, for example, 150 C. under high vacuum, say, 10* millimeters of mercury for a-period of ,one hour. In contrast, the products of my invention are stable undersuch treatment. Neither can the ester groups be removed by washing with hot methyl ethyl ketone .or similar solvents or by prolonged extraction in a Soxhlet extractor. In case of ordinary physical adsorption the alcohol is displaced by such treatment.

The products of the invention are useful as selective adsorbents and as fillers for plastic material, wherein the silica surface has been rendered compatible to the plastic medium by the presence of a functional group which has a similar counterpart in the structure of the organic polymer. For instance, a cya-no alcohol can be used as a filler in polyacrylonit-r-i-le polymers, and a halogen substituted alcohol can be usedas a filler i-n vinyl or vinylidine chloride plastics. The products have a special adsorption affinity for organic compounds in which there is an active hydrogen, such as chloroform, methylene chloride and other hydrogen bonding agents and particularly for eth-ylenically unsaturated hydrocarbons. The products are also useful as fillers for synthetic rubbers and particularly for the silicone type rubbers.

The invention will-be better understood by reference to the following, illustrative examples:

Example 1 This is an example of a process of this invention wherein a siliceous solid is esterified with an alcohol containing a halogen atom.

A silica powder is obtained by the gelation of a commercially available 30% silica sol consisting of 1.7 millimicron colloidal particles and known as Ludox colloidal silica and by drying the resulting gel at a temperature of C. for a period of twenty-four hours at a pH of about 4.5. Products of this character are described and claimed in the copending application of Max F. Bechtold and Omar E. Snyder, Serial No. 256,142, filed November 13, 1951, now abandoned.

The dried material, which is in the form of coherent aggregates of dense, ultimate units of amorphous silica,

is dispersed to a free-flowing powder .by the use of a micropulverizer.

A portion of the aforementioned powder is heated in a muffle furnace in the presence of air for a period of two hours at a temperature of 600 C. in accordance with the invention described and claimed in the .copending U. S. application .of Warren K. Lowen, Serial No. 261,139, filed December 11, 1951. The heat treatment activates the siliceous surface towards reaction with an alcoholic group.

The activated silica is refluxed for a period of about two hours with ethylene chlorohydrin at a temperature of about C. The silica-ethylene chlorohydrin mixture is filtered. The silica is collected, washed exhaustively with ether and vacuum-dried at a temperature of 100 C. for a period. of about sixteen hours.

The physical appearance of the resulting product is substantially unchanged from that of the unesterified free-flowing powder. Chemical analysis of the product shows the silica to contain 1.07% carbon. Its surface area as measured by nitrogen adsorption is about 175 m. /g., which corresponds. to a surface coverage of about ethoxygroups per 100 squaremillimicrons of surface. The presence of chlorine substituted groups is also shown by chemical. analysis.

Example 2 The following is tan example of an esterification of a silica with an alcohol containing a nitrile group:

A sample of dried silica substantially identical with that described in Example 1 is heated in a muflie furnace in the presence of air at a temperature of 600 C. for a period of about one hour. Following the heat activation treatment, the silica is slurried in beta-hydroxypropionitrile. The slurry is refluxed for a period of two hours at a boiling point of the nitrile, which is about 190 C. The esterified silica is collected by filtration, exhaustively washed with ether and then vacuum-dried at a temperature of 100 C. for a period of sixteen hours. It is a free-flowing white powder.

Upon chemical analysis, the product is found to contain 1.46% carbon and 0.49% nitrogen. It has a surface area of 175 m. g. which corresponds to a surface coverage of about 120 oxypropionitrile molecules per 100 square millimicrons of surface area.

Example 3 This example shows the esterification of a siliceous solid with a nitro-substituted alcohol.

A portion of dried Ludox colloidal silica is heated at a temperature of 600 C. for a period of about one hour in order to activate it. The activated material is then heated for a period of two hours with an excess of p-nitrobenzyl alcohol, the temperature being maintained between 150 and 175 C. The organic phase becomes very dark during heating.

The silica is collected by filtration, washed with acetone and vacuum-dried at a temperature of 102 C. The resulting powder is white. Chemical analysis of it showed 3.85% carbon and 0.49% nitrogen to be present on the surface. This analysis corresponds to a degree of esterification of about 120 p-nitrobenzoxy groups per 100 square millimicrons of surface area, based on a surface area of about 175 square meters per gram for the silica.

Example 4 The following is an example of a product of this invention which is obtained by the esterification of a siliceous solid with a hydroxy-substituted ester:

A portion of Ludox colloidal silica described in Example 1 is heated for a period of about one hour at a temperature of 600 C. The resulting activated silica is cooled and then slurried with an excess of beta-hydroxyethyl acetate. The slurry is stirred for a period of two hours at a temperature of from 150 to 170 C.

The silica-ethyl betahydroxyacetate mixture is filtered and the siliceous product is collected. The product is washed and dried in vaccum. It contained 3.43% carbon, which corresponds to a degree of esterification of about 245 molecules per 100 square millimicrons of surface.

Example 5 This is an example of a process of the invention in which finely-divided, precipitated reinforced aggregates of silica are esterified with monobutyl ether of ethylene glycol.

A water-wet filter cake containing about 6% silica in the form of finely-divided, precipitated, reinforced aggregates of silica is prepared in the following manner:

A 425-pound portion of a sodium silicate solution containing 2.39 grams of SiOz per milliliters of solution and having a molar SiOzzNazO ratio of 3.25:1 is charged to a 100-gallon steel tank equipped with a one-half horsepower, 400 R. P. M. Lightnin mixer driving a 10" diameter, three-bladed propeller. The silicate is heated to a temperature of 35i2 C. by steam-injection. A sufficient amount (about 162 pounds) of a solution containing 2.40 per cent sulfuric acid is added uniformly over a period of about 30 minutes to bring the pH to 9.7:02 as measured at 25 C. During this period the temperature of the reacting mass is maintained below 40 C.

The amount of acid added during the aforementioned step of the process is equivalent-to about of the NaaO in the original sodium silicate. The sodium ion content remains below 0.3 N throughout the process. The clear sol thus obtained is heated to 95 C. in about fifteen minutes. After heating, the sol contains discrete ultimate silica units which are. about 5-7 millimicrons in diameter. The sol has a pH of about 10.1. I

Solutions of sodium silicate and sulfuric acid are then added simultaneously at a uniform rate over a period of two hours through inlets located close to the vortex formed by the agitator. An 85.4-pound portion of the sodium silicate solution is used, which contains 13.22 grams of SiOz per 100 milliliters of solution and has a molar SiOzzNazO ratio of 3.25:1. -The sulfuric acid is a 4.65 per cent aqueous solution and is added in an amount to maintain the pH of the reaction mixture at 103:0.2 as measured at 25 C. throughout the course of the reaction. Such an amount is sufiicient to neutralize about 80% of the NazO in the silicate solution and maintain the sodium ion concentration below 0.3 -N throughout the process. The temperature is maintained at 95 C. throughout the addition of acid and silicate.

During the heating of the initial sol the tiny, discrete particles of the sol increase in size. Then, during the initial addition of silicate and acid they may become chemically bound together in the form of open networks or coherent aggregates of supercolloidal size, wherein the colloidal particles are present as dense ultimate units. The aggregates are precipitated. In the subsequent simultaneous addition of silicate and acid the aggregates are reinforced. Since about one part of silica is added for each part of silica in the original sol, the build-up ratio on the aggregates is about 1:1.

Still maintaining a temperature of 95 C. the pH of the solution is adjusted from 10.3 to 5.0 by adding 4.65 per cent sulfuric acid at a rate of about 0.24 gallon per minute for 20 minutes and then adding small portions followed by repeated pH determinations until the pH is 5 as measured at 25 C. This requires about 32 pounds of the sulfuric acid solution.

The slurry thus obtained is then maintained at a temperature of from to C. without agitation for a period of four hours. This is to further coagulate the precipitate to aid in filtration. The precipitate is filtered in several portions on a SO-gallon Nutsche, using nylon cloth as a filter medium. The filter cake is washed on the filter with fixe displacements of cold water and then sucked as dry as the apparatus permits; The final filter cake contains between 6 and 7 per cent solids. Its pH is adjusted to a pH of 2 to 3. The filter cake is then stored.

A 400-gram portion of the cake is reslurried in water and adjusted to a pH of 5.5 with sodium hydroxide. The resulting slurry is filtered. The wet cake is collected and mixed with 800 grams of monobutyl ether of ethylene glycol.

The resulting slurry is transferred to a flask fitted for distillation. Water is removed by distilling continuously until the temperature in the distilling pot reaches about 148 C. At this point the water content of the supernatant material is about 0.14 per cent.

Esterification of the silica with the monobutyl ether of ethylene glycol is effected by autoclaving the silicabutyl cellosolve mixture at a temperature of 300 C. for a period of one-half hour under autogenous pressure. The reaction mixture is cooled, filtered, and the surfaceesterified silica collected and dried at 140 C. in a vacuum oven.

The resulting dry, white, free-flowing powder is found upon analysis to contain 9.61 per cent carbon. This percentage corresponds to a surface coverage of about 280 ester groups per square millimicrons of surface.

A portion of the product is milled into oil and a grease is formed. Q

11 Example ,6

This example illustrates a process of my invention in which a filter cake of silica is reacted with 'monohexyl ether of ethylene glycol.

A 200 gram portion of the silica filter cake, whose preparation is fully described in Example 5, is adjusted to a pH of :5. The cake is transferred to a vessel containing 350 grams of the mono-n-hexyl ether of ethylene glycol. The resulting slurry is charged to a distillation apparatus; Water is removed by distillation by increasthe pot temperature to about 180 C. A sample of the supernatant liquid is found to contain 0.65 per cent water by chemical analysis.

The slurry is autoclaved" at a temperature of 300 C. for thirty minutes in order to ellect esterification'. The resulting esterified product is collected by filtration and dried in a vacuum oven at a temperature of 130 C.

The surface esterified silica powder is a white, freeflowing material. I-ts carbon analysis shows 18.95 per cent carbon which corresponds to 416 ester groups per 100 square mill-imicrons of surface.

I claim: I

-l'. A solid consisting essentially of substrate particles of inorganic siliceous material having an average specific surface area of from I to 900 square meters per gram, and an average particle diameter greater than about 1 millimicron having chemically bound to the silicon atoms on the surface of said particles at least 100 -OR groups per 100 square millim-icrons-of surface area of the siliceous material, where R is a substituted hydrocarbon radical in which the carbon attached to oxygen is also attached to at least one hydrogen atom, said substituted hydrocarbon radical having a neutral-reacting electron donor electronegati-ve atom attached to a carbon atom at least 1 carbon atom removed from the oxygen atom of the OR group, the electronegative atom being selected'from the class consisting of nitrogen, oxygen and halogens having an atomic number above 9', each R radical having from 2 to '18 carbon atoms.

2. A pulverulent solid consisting essentially of subtrate particles of inorganic siliceous material in a supercolloidal state of subdivision having an average specific surface area of at least 1 square meter per gram, and an average particle diameter greater than about 1 millimicron having :hemically bound to the silicon atoms on the surface of said particles at least 100' OR groups per 100 square millimicrons of surface area of the siliceous material, where R is'a substituted'hydrocarbon radical in which the carbon attached to oxygen is also attached to at least one hydrogen atom, said substituted hydrocarbon radical having a neutral-reacting electron donor electronegative atom attached to a carbon atom at least 1 carbon atom removed from the oxygen atom of the -OR group, the electronegative atom being selected from the class consisting of nitrogen, oxygen and halogens having an atomic number above 9, each R radical having from 2 to 18 carbon atoms- 3. A- powder consisting essentially of subtrate particles of amorphous silica in a supercolloidal state of subdivision having an. average specific surface area of from 25 to 900 square meters per gram, and an average particle diameter greater than about 1 millimicron having chemically bound to the silicon: atoms on the surface of said particles at least 100-OR groups. per 10.0 square millimicrons of surface area of substratesurfacc, where R is a substituted hydrocarbon radical in which the carbon attached to oxygen is also attached to at least one hydrogen atom, said substituted hydrocarbon radical having a neutral-reacting electron donor electromegative atom attached to a caraon atom at least 1 carbon; atom. removed from the axygen atom of the OR group, the electronegative atom Jeing selected from the class consisting of nitrogen, oxygen and halogens having an. atomic number above 9, each R radical having from 2 to 18 carbon atoms.

4. A powder consistingessentially of substrate particles of amorphous silica in a supercolloidal state of subdivision having an average specific surface area of from 20.0 to 900 square meters per gram, and an average particlediameter greaterthan about 1 millimicron having an average pore diameter of at least 4 millimicrons, and having chemically bound .to the silicon atoms on the surface .of said. particles at least OR groups per 100 square millimicrons of surface area of the siliceous material, where R is .a substituted hydrocarbon radical in which the carbon attached to oxygen is also attached to atleast one hydrogen .atom, said substituted hydrocarbon radical having a neutral-reacting electron donor electronegative atom attached to .a carbon atom at least 1 carbon atom removed from the oxygen atom of the OR group, the elcctronegative atom beingselected from the class consisting of nitrogen, oxygen and halogens having an atomic number above 9, each Rradical having from 2 to 18 carbon atoms.

'5. A process which comprises the step of chemically reacting an alcohol of the formula ROH in which R is a substituted hydrocarbon radical having from 2 to 18 carbon atoms, wherein the carbon atom attached to oxygenis also attached to at least one hydrogen, said radical containing a neutral-reacting electron donor substituent group attached to a carbon atom at least 1 carbon atom removed from the hydroxyl group, the substituent group containing at least one electronegative atom selected from the class consisting of nitrogen, oxygen and halogens hav:

. ing an atomic number above 9, the alcohol being suiticiently neutral that the pH of a 1% aqueous solution is between 5 and 8' as measured by immersion of a glass electrode, with an inorganic siliceous material having an average specific surface area of from 1 to 900 square meters per gram, and an average particle diameter greater than about 1 millimicron and having a reactive surface containing groups selected from the class consisting of silanol and heat-activated silicon-oxygen groups, while maintaining the water content of the system below about 5 per cent by weight of the alcohol in the system and the temperature in the range from 100 C. to the thermal decomposition temperature of the alcohol.

6. A process which comprises the step of chemically reacting at a temperature of at least 100 C. an alcohol of the formula ROH in which R is a substituted hydrocarbon radical having from '2' to 18 carbon atoms, wherein the carbon atom attached to oxygen is also attached to at least one hydrogen, said radical containing a neutral-reacting electron donor substituent group attached to a carbon atom at least. 1- carbon atom removed from the hydroxyl group, the substituent group containing at least one electronegative atom selected from the class consisting of nitrogen, oxygen and halogens having an atomic number above 9, the alcohol being sufficiently neutral that the pH of a' 1% aqueous solution is between 5 and 8 as measured by immersion of a glass electrode, with an inorganic siliceous material in a supercol'loidal state of subdivision, having an average specific surface area of from 1 to 900 square meters per gram and an average particle diameter greater than about 1 millimicron and having a reactive surface containing groups selected from the class consisting of silanol and heat-activated silicon-oxygen groups, while maintaining the water content of the system below about 5 per cent by weight of the alcohol in the system and the temperature in the range from 100 C. to the thermal decomposition temperature of the alcohol.

7. A process which. comprises the step of chemically reacting an alcohol of the formula ROH in which R is a substituted hydrocarbon radical having from 2 to 18 carbon atoms, wherein the carbon atom attached to oxygen is also attached to at least one hydrogen, said radical containing a neutral-reacting electron donor substituent group attached to a carbon atom at least 1 carbon atom removed from the 'hydroxyl group, the substituent group containing at least one electro-negative atom selected from the class consisting of nitrogen, oxygen and halogens having an atomic number above 9, the alcohol being sulficiently neutral that the pH of a 1% aqueous solution is between 5 and 8 as measured by immersion of a glass electrode, with an inorganic siliceous material in a supercolloidal state of subdivision, having an average specific surface area of from 1 to 900 square meters per gram, and an average particle diameter greater than about 1 millimicron and having a reactive surface containing groups selected from the class consisting of silanol and heatactivated silicon-oxygen groups, while maintaining the water content of the system below about 5% by weight 5 organic siliceous solid are chemically bound thereto.

References Cited in the file of this patent UNITED STATES PATENTS 10 2,395,880 Kirk Mar. 5, 1946 2,438,379 Archibald et a1. Mar. 23, 1948 2,454,941 Pierce et a1 Nov. 30, 1948 

1. A SOLID CONSISTING ESSENTIALLY OF SUBSTRATE PARTICLES OF INORGANIC SILICEOUS MATERIAL HAVING AN AVERAGE SPECIFIC SURFACE AREA OF FROM 1 TO 900 SQUARE METERS PER GRAM, AND AN AVERAGE PARTICLE DIAMETER GREATER THAN ABOUT 1 MILLIMICRON HAVING CHEMICALLY BOUND TO THE SILICON ATOMS ON THE SURFACE OF SAID PARTICLES AT LEAST 100 -OR GROUPS PER 100 SQUARE MILLIMICRONS OF SURFACE AREA OF THE SILICEOUS MATERIAL, WHERE R IS A SUBSTITUTED HYDROCARBON RADICAL IN WHICH THE CARBON ATTACHED TO OXYGEN IS ALSO ATTACHED TO AT LEAST ONE HYDROGEN ATOM, SAID SUBSTITUTED HYDROCARBON RADICAL HAVING A NEUTRAL-REACTING ELECTRON DONOR ELECTRONEGATIVE ATOM ATTACHED TO A CARBON ATOM AT LEAST 1 CARBON ATOM REMOVED FROM THE OXYGEN ATOM OF THE -OR GROUP, THE ELECTRONEGATIVE ATOM BEING SELECTED FROM THE CLASS CONSISTING OF NITROGEN, OXYGEN AND HALOGENS HAVING AN ATOMIC NUMBER ABOVE 9 EACH R RADICAL HAVING FROM 2 TO 18 CARBON ATOMS.
 5. A PROCESS WHICH COMPRISE THE STEP OF CHEMICALLY REACTING AN ALCOHOL OF THE FORMULA ROH IN WHICH R IS A SUBSTITUTED HYDROCARBON RADICAL HAVING FROM 2 TO 18 CARBON ATOMS, WHEREIN THE CARBON ATOM ATTACHED TO OXYGEN IS ALSO ATTACHED TO AT LEAST ONE HYDROGEN, SAID RADICAL CONTAINING A NEUTRAL-REACTING ELECTRON DONOR SUBSTITUENT GROUP ATTACHED TO A CARBON ATOM AT LEAST 1 CARBON ATOM REMOVED FROM THE HYDROXYL GROUP THE SUBSTITUENT GROUP CONTAINING AT LEAST ONE ELECTRONEGATIVE ATOM SELECTED FROM THE CLASS CONSISTING OF NITROGEN, OXYGEN AND HALOGENS HAVING AN ATOMIC NUMBER ABOVE 9, THE ALCOHOL BEING SUFFICIENTLY NEUTRAL THAT THE PH OF A 1% AQUEOUS SOLUTION IS BETWEEN 5 AND 8 AS MEASURED BY IMMERSION OF A GLASS ELECTRODE, WITH AN INORGANIC SILICEOUS MATERIAL HAVING AN AVERAGE SPECIFIC SURFACE AREA OF FROM 1 TO 900 SQUARE METERS PER GRAM AND AN AVERAGE PARTICLE DIAMETER GREATER THAN ABOUT 1 MILLIMICRON AND HAVING A REACTIVE SURFACE CONTAINING GROUPS SELECTED FROM THE CLASS CONSISTING OF SILANOL AND HEAT-ACTIVATED SILICON-OXYGEN GROUPS, WHILE MAINTAINING THE WATER CONTENT OF THE SYSTEM BELOW ABOUT 5 PER CENT BY WEIGHT OF THE ALCOHOL IN THE SYSTEM AND THE TEMPERATURE IN THE RANGE FROM 100*C. TO THE THERMAL DECOMPOSITION TEMPERATURE OF THE ALCOHOL. 